The VTG voltage is the supply voltage to the target AVR microcontroller. It is connected to the AVR's VCC pin. VTG can either be generated by STK600, or it can be supplied from an external source.
The on-board VTG source is set from AVR Studio. To use this source, the VTARGET jumper must be mounted. The on-board supply can be adjusted from 0.9 to 5.5V in steps of 0.1V.
VTG can also be set to 0V, but due to hardware limitations, onboard generated VTG can not be set between 0 and 0.9V.
Note: Always check the AVR datasheet for operating voltage range before adjusting VTG.
When STK600 is powered through the USB cable approximately 300 mA can be delivered to the target section.
If the VTARGET jumper is removed, VTG must be supplied from an external source. Connect the external source to one of the VTG pins on any of the PORT headers. Always connect common ground (GND) when using an external VTG voltage.
When using an external source, the user must ensure that VTG is larger than any of the AREF voltages.
Note: The kit must always be powered when using an external VTARGET supply. If VTG voltage is supplied from an external source while the main power switch is in the off position the kit may become damaged.